1. Field of the Invention
This invention relates to hair care compositions, and, more particularly, to hair repair compositions for mending damaged fibers such as split ends of hair fibers.
2. Description of the Prior Art
The technical term for split ends is trichoptilosis. It is defined as a longitudinal splitting of the hair fiber which develops after the protective cuticle has been stripped away from the end of the hair fibers as a result of either physical or chemical traumatizing of the hair. Formation of split ends develops because of the fine structure of hair and the forces that are at work in its components.
There is a sequence of mechanical events that occur in the formation of split ends. During the combing process, fibers tend to snarl as the comb approaches the tip ends of the hair. It can be observed in these entanglements that the fibers are bent to various degrees. Since hair is elliptical and has a major and a minor axis, this bend occurs parallel to the major axis. The bending effect subjects the hair to longitudinal shear stresses parallel to the major elliptical axis. The magnitude of these shear forces are parabolically distributed across the minor axial diameter of the elliptical section. As hairs are being bent, these shear stresses will result in fracture and will propagate along the major elliptical axis resulting in a split end. The fibers bend as they pass through the prongs of a comb.
The disulfide bond in hair is another factor in split end formation. Protein molecules in the cortex of the hair fiber are crosslinked by covalent disulfide bonds, which provides strength and flexibility. During chemical processing, or through environmental damage, these bonds tend to break which makes the hair more susceptible to mechanical damage. The result is that damaged hair is more prone to splits and cracks during the combing and brushing process.
Split ends are more prone in hair that has been damaged by weathering, chemical treatments, or mechanical damage. Prevention of split ends generally involves adding lubricity to the hair with cationic surfactants so that there is less friction during combing resulting in less snarling. Also, adding plasticizing agents, which allows the hair to bend with more facility, will reduce split ends. Since water is a plasticizing agent, it is expected that fewer split ends will be produced at a high relative humidity, particularly, with the application of humectants that allows for moisturization.
Lubricating agents that can prevent or minimize formation of split ends include cationic surfactants commonly found in creme rinses, e.g. cetrimonium chloride, stearalkonium chloride, dicetyldimonium chloride, and behentrimonium methosulfate. Cationic polymers are more common lubricating agents found in shampoos. These polymers include polyquaternium compounds such as polyquaternium-6, -7, -10, -11, and -28. Guar hydroxypropyltrimonium chloride also is used as a lubricant. The mechanism by which such conditioner reduces damage during combing is based upon lubricity. The lubrication reduces the friction in the hair during combing and hence reduces the strength of the abrasive forces to which the hair is being subjected. This in turn reduces the number of entanglements during the combing process.
Plasticizing agents including humectants such as glycerin, propylene glycol, acetamide MEA, and sorbitol also are used for this purpose. An example of a substantive humectant containing a positive charge is Quaternium®-22 (Ceraphyl® 60). By treating the hair with conditioners that provide these properties it is possible to prevent the formation of split ends.
This invention, however, is concerned with split end repair and mending rather than prevention.
Prior Methods of Producing and Assessing Prevention of Split Ends
A mechanical device has been described in the literature to generate split ends. It consists of a motor driven rotary arm to which two combs are attached. A hair swatch is clamped into place so that the ends of the hairs are struck by the rotary arm. A linear relationship was established by Cooper between the time of exposure and the number of split ends generated. Hair treatment such as shampoos, conditioners and mousses reduced the number of split ends produced, however, studies are not conducted to affect their repair. Prevention was determined by comparing the percentage of hairs split in the hair swatches that were treated with different conditioning preparations. No explanation was provided, however, as to how this percentage is derived, or whether it is based on a sample of fibers from the tress or based on all the fibers in the tress.
Kon et al in J. Cosmet. Sci. 20, 361-380 (1998) also developed a method for artificially inducing damage to hair in order to serve as a model for studying the effect of ingredients on hair damage. Two models are described, one for scale lift and one for split hair, both having their own characteristic method. The split hair model consists of soaking the hair in a reducing solution that extracts a certain quantity of cortical protein from the hair fiber. After a detailed procedure of washing, de-lipidation, drying, reducing, washing, re-oxidizing, and lyophilizing (freeze-drying), the hairs are viewed for splits with an SEM. They postulated that the driving force for the split is osmotic shock. With this technique it was found that keratin peptides and cationic hydroxyethylcellulose have a preventative effect on split formation. These test solutions are added in between the reducing and oxidizing steps of the test method. Their explanation for adding these ingredients in the middle of the process is the fact that they prevent expansion of the split hairs during the lyophilization stage. They mention that peptides of low molecular weight can do this because they are more penetrative, and cationic derivatives because of their high affinity for the cortical proteins. Kon mentions that the method by Cooper has low reproducibility.
Split End Repair and Prevention Methodology
U.S. Pat. No. 6,071,505 described a water soluble quaternary ammonium cellulosic derivative of controlled charge density. It mentions many uses of these novel compounds applicable in both hair and skin care products. One such use is that it can mend split ends. However, no substantiation was given in the patent and there is no test method revealed as to how split end mending is achieved.
A brochure by Amerchol Corporation stated that all grades of UCARE® Polymer can mend split ends. The method described is as follows. “ . . . individual strands of virgin brown hair were mounted on a plastic stand for each shampoo to be tested. Each hair was then shampooed by inserting the individual hair into an eyedropper containing the test formulation. The strand was then rinsed with distilled water from a squeeze bottle and the process was repeated to simulate normal shampoo procedure. The hairs were examined immediately by hand lens for mended splits, and again after drying one hour at 54° C. (129° F.). To simulate combing, each hair was “tickled” ten times with a spatula and the number of splits still mended was recorded. After one hour at room temperature, the hairs were again examined.” Results indicate that at every stage of the experiment, UCARE® Polymer containing shampoos provide for 100% mending of split ends. The control shampoo containing just TEA Lauryl Sulfate and Cocamide DEA provided for 70% mending. With this method the combing simulation did not subject the hair to enough stress that actual combing provides. Also, the 70% mending rate for the control shampoo is too high suggesting that the tickling does not provide enough stress on the fiber that actual combing does to reopen the split end.
U.S. Pat. No. 6,258,348 described a hair conditioning composition specifically for mending split ends. The composition consists of a ternary mixture of guar (cationic or amphoteric), a betaine based polyurethane surfactant, and a silicone polyurethane. This ternary blend can be incorporated into a cream rinse or a 2-in-1 shampoo to effectively mend split ends. The test method used to support mending for the example formulations in the patent consists of selecting ten split end fibers from a tress and then attaching them to a single tab tress. The single tab tress with the split end fibers are then subjected to the treatment such as shampooing and left to air dry. Split end repair is then evaluated under a magnifying glass. Percent mending is then reported. Their findings indicate that a high percentage of mending occurs with 2-in-1 shampoos containing a ternary blend of ingredients compared to the same composition with only two of the three components. One drawback with this method is that the permanence of the mend was not studied, only the initial mending. Also, combing ten fibers is not a realistic amount of hair that would impart enough stress during the combing process.
U.S. Pat. No. 4,900,545 described that a composition of panthenol, glucose, PVP and phytantriol could regenerate hairs that have been split. This result was tested on 100 hairs all of which had been split by mechanical or electrostatic pretreatment. The hairs were treated 10 minutes with the undiluted preparations of examples 1 through 7 therein. The hairs were then rinsed with tap water, dried and combed. The visually discernable split ends remaining were then determined by counting. The percentage of split ends remaining for the 7 formulas ranged from 10 to 50%. This method suffers because 100 fibers is not a sufficient mass of fibers when passed through the comb to subject the hair to sufficient bending to cause the hairs to split.
U.S. Pat. No. 6,251,379 disclosed that hair compositions containing a combination of quaternized keratose and a defined silicone derivative can mend split ends. The method to substantiate this effect consisted of using bundles of Asian type hair, treating them with the composition, and drying with combing and blow drying. The hair is then brushed another ten times. Split end mending is assessed both before and after treatment. Although there is a standard for judging the degree of the prevention of re-splitting, it appears that the assessment is qualitative in nature. One positive with this method, however, is the fact that it assesses split end repair after the hair is brushed.
U.S. Pat. No. 6,139,851 described that a hair cream based on a lower alcohol in oil type emulsion containing silicone derivatives to mend split ends. The method is the same as is described in U.S. Pat. No. 6,251,379. No quantitative assessment of split end repair was described suggesting to a greater extent than the previous patent that a qualitative assessment of split end repair was used.
Ramachandran in WO 96/32920 described an improved hair rinse composition. They claim that their hair rinse composition not only conditions hair to provide such properties as wet detangling, but also lends fixative properties and repairs split ends. The three main ingredients that comprise the rinse are quaternary ammonium salts, water insoluble acrylic or acrylate polymers and a solvent that comprises a long chain alcohol and/or alcohol ethoxylate. The solvent was used to compatibilize the quat and polymer. It is theorized, but no proof is shown, that the quaternary surfactant and polymer form a complex with each other in the solvent. It was also theorized that this complex is deposited during the rinse cycle of this hair conditioning composition which provides the function of both conditioning and styling that normally are contradictory to one another when formulated in the same product. Proof of this is supplied by running panel tests on hair swatches for ease of combing and stiffness in hair characteristic panel studies using tresses. It was found in all cases that high scores are obtained for these two hair characteristics when hair was treated with rinses containing the quat-polymer-solvent complex.
Split end mending also was measured therein using a Salon panel study. The procedure consisted in essence of a cycle of washing, drying, counting, treating, combing and counting. Counting split ends consisted of bundling the hair on the head in discrete sections. Using magnifying binoculars, 100 hairs were counted in each section and the number of split ends calculated for the whole head. Experimental results proved that the rinse containing the complex mended split ends. It was also determined that the degree of split end mending was dose related and increased with the number of treatments. They theorized that split end mending is achieved by the adhesiveness of the polymer. The thin layer of polymer that remains on the inner surfaces of the split ends after drying holds the splits together. The method relies heavily on counting split end fibers and statistical analysis of the data.